The click noise is a commonly known effect which occurs in applications of e.g. FM radio receivers which may be caused by multi-path effects. These click noises are not accepted by users of such FM radio receivers and therefore it is of interest to reduce or delete such click noise.
WO 98/42081 discloses an adaptive multi-path filter which eliminates audibly objectionable click noise generated at the output of an FM discriminator to prevent audible distortion or other corruption of the desired signal which may include voice and low speed digital data. Clicks are detected at the discriminator output using a colored-noise, matched filter designed and adapted to the click signature/shape as well as to the desired signal characteristics. The colored-noise matched, filter output is then compared to an adaptive threshold. When the threshold is exceeded, a click is registered as detected. Click duration is then estimated. An estimate of the desired signal is generated and that replaces the originally received data signal estimate within the click duration region. Using characteristics of the desired signal just before and after the detected click noise, the adaptive filter accurately estimates the parameters of the desired signal so that the replacement signal fairly models what the desired signal would have looked like had the click not occurred. In this way, a substantial portion of the desired signal is preserved.
JP 09-083384 discloses a reception intensity detection part which compares each reception intensity with a prescribed value, furthermore it contains a voice level detection part and the voice level is compared with a prescribed value. Each voice level is compared with a prescribed value by the decision part and when the level is higher than the prescribed value, the output is performed. An AND gate performs an output when the simultaneous outputs from the both of the decision parts exist. In a mute control part, an incorporated timer is started by the output from the AND gate. For a fixed time after the output of the AND gate is released, a mute signal is outputted to a digital attenuator for preliminarily set time. The voice output for the period is stopped or is attenuated up to a prescribed level.
JP 10-013261 discloses that a bit error rate measurement takes place and in case the bit error rate exceeds a certain limit, a bit error rate discrimination circuit outputs a mute request signal. A tail end of the mute request signal is extended by using a delay circuit and an OR circuit, to generate an extended mute request signal. A digital voice signal is delayed by a time required for a bit error rate measurement period and a bit error rate discrimination at a delay circuit and outputted via a latch circuit, and while the extended mute request signal is set, the input data are stored by a latch circuit.